Disposal, clean-up and/or site remediation of hazardous carbon containing compounds continues to be a challenge, especially for organic compounds that are difficult to oxidise or are "non-oxidizable". J. Hoigne and H. Bader, OZONATION OF WATER: SELECTIVITY AND RATE OF OXIDATION OF SOLUTES, Ozone: Science and Engineering, Vol. 1, pp 73-85, 1979 identify the following compounds as "not [be] oxidized directly by ozone even during an extended ozonation": chloroethylenes including specifically tetrachloroethylene, and trichloroethylene, benzene, aliphatic alcohols, aldehydes, carbonic acids, specifically oxalic acid. Other non-oxidizable compounds include but are not limited to carbon tetrachloride (CCI.sub.4), methylisobutylketone (MIBK) also known as hexone, 4-methyl-2-pentanone, perchloroethylene (PCE), and pentachlorophenol (PCP).
Research in this field has been ongoing for many years. In the paper TREATMENT OF LIQUIDS WITH ELECTRIC DISCHARGES, W. L. Hudson, The American Institute of Chemical Engineers, 1979, various embodiments of "plasma reactors" are shown and discussed. The reactors tend to have the common features of one electrode positioned above or away from the liquid containing the carbon containing compound to be treated and a second electrode in contact with the liquid containing the carbon containing compound to be treated. However, Hudson states
The only encouraging success with the treatment of liquids with electric discharges has been in a partial vacuum at or near the vapor pressure of the liquid being treated, more specifically in the pressure range 20 to 70 mm of Hg. If the pressure is less than the vapor pressure of the liquid being treated, the liquid boils, sometime violently. If the pressure increases as a result of gas buildup in the system the discharge might extinguish itself and at best becomes much less efficient.
Hudson does, however, report a test using pulsed discharge at 1 atmosphere pressure. Hudson reports percent reacted of a carbon containing compound as ranging from 7 percent reacted to 92 percent reacted. Compounds reacted were Fe.sup.++, and carbon containing compounds reacted of phenol, sewage, and acrylonitrile.
In an article of the Journal of Chemical Society, GLOW DISCHARGE ELECTROLYSIS. PART I. THE ANODIC FORMATION OF HYDROGEN PEROXIDE IN INERT ELECTROLYSIS, R. A. Davies, A. Hickling, pp 3595-3602, 1952, the authors studied the formation of hydrogen peroxide using glow discharge. They observed the influence of varying electrical current, volume of anolyte, surface area, electrode distance, size and shape of electrode, type of gas atmosphere (air, N.sub.2, O.sub.2, H.sub.2, N.sub.2 O), pressure and type of electrolyte. For type of gas atmosphere, they found no difference in the amount of peroxide production. In a second article in the Journal of Chemical Society, GLOW DISCHARGE ELECTROLYSIS. PART II. THE ANODIC OXIDATION OF FERROUS SULFATE, A. Hickling, J. K. Linacre, pp 711-720, 1954, ferrous sulfate oxidation was studied by varying the same parameters as had been done for hydrogen peroxide formation. Again, it was found that varying the atmosphere from N.sub.2 to H.sub.2 had no appreciable effect. A minor effect was observed for O.sub.2 atmosphere.
In a report, HAZARDOUS WASTE REMEDIAL ACTIONS PROGRAM ANNUAL PROGRESS REPORT, R. B. Craig, DOE/HWP-102, Martin Marietta Energy Systems, Inc., August 1990, pp 121-125, there is described tests in which air ions, specifically O.sub.2.sup.-, are used to destroy acrylamide, chlorobenzene, styrene, phenol, benzene, methoxychlor, 2,4-dichlorophenol, chloroform, benzoic acid, and citric acid.
In a paper, THE DEGRADATION OF ORGANIC DYES BY CORONA DISCHARGE, S. C. Goheen et al., Chemical Oxidation: Technology for the 90's Conference February 1992, a corona discharge reaction vessel is shown with one electrode suspended above a liquid surface and a second electrode in contact with the liquid. Electricity was applied from 5-15 kV, 10 to 50 .mu.A to degrade organic dyes, specifically Malachite Green, New Coccine, methylene blue, and silicic acid. Air and nitrogen were used and found to influence the amount of electrical current needed, but with no effect on chemical reaction rate, except that oxygen was necessary. There was no reaction with only nitrogen and reaction rate increased with increasing oxygen concentration, thereby concluding that "oxygen is clearly required for the dye to react with species generated by corona discharge".
Corona discharges are relatively low-power electrical discharges that can be initiated at or near ambient conditions. The corona is in the gas phase and, when generated with an electrode above a liquid surface and an electrode in contact with the liquid, the corona is also immediately on the liquid surface. It should be noted that corona discharge is not merely another configuration of electrolysis where chemical reactions are accomplished by charge transfer oxidation and reduction. Hickling et al. (cited above) proved that charge transfer is only a minor factor in corona discharge and that the chemical effects are fundamentally different. Most noticeably, many equivalents of chemical reaction can be accomplished for each electron of charge transfer. Each electron accelerating through the electric field collides with many gas molecules creating other charged particles and neutral active species (free radicals and atoms). Depending on the conditions of the discharge active species accounting for between 8 and 180 reactions have been measured for each electron of charge transferred. These can bring about ionization, excitation or dissociation of solvent molecules by collision, in addition to charge transfer reactions observed in a typical electrochemical process.
Corona discharge is most similar to radiolysis or electron beam processes and the concepts and ideas developed in radiation chemistry can be directly applied to this type of corona discharge process as pointed out in by Hickling in his book THE MECHANISM OF CHARGE TRANSFER, Chapter 5, "Electrochemical Processes in Glow Discharge at the Gas-Solution Interface", pp. 328-373. However, there are some noteworthy differences between the two processes. For example, although the energy per electron in corona discharge is relatively low (.about.100 eV) as compared to most ionizing radiation (.about.10.sup.4 -10.sup.7 eV), the dose rate can be extremely high. It was measured by Hickling et al., that for a current of 0.075 A, the number of singly charged gaseous ions reaching the solution surface per minute was 2.8.times.10.sup.19. Assuming an average energy of 100 eV, the dose rate for corona discharge amounts to 2.8.times.10.sup.21 eV min.sup.-1. This is significantly higher than the dose rate normally used in radiolysis (.about.10.sup.16 -10.sup.20 eV cc.sup.-1 min.sup.-1). Therefore, the amount of chemical change which can be affected in corona discharge is much greater than that in radiolysis, and high concentrations of substrate can be used. Furthermore, under these conditions, impurities seem to have much less effect (Hickling, ELECTROCHEMICAL PROCESSES IN GLOW DISCHARGE AT THE GAS SOLUTION INTERFACE, pp 329-373, J. of Electroanalytical Chemistry, 1964). Thus, corona discharge is distinct from typical electrochemical processes because it can bring about chemical changes which are similar to those which result from ionizing radiation. Corona discharge is also distinct from radiolysis because the energy input is of the order of an electrochemical process.
The research described above has not resulted in a corona discharge method and apparatus that is capable of cost effectively removing hazardous carbon containing compounds from water, or destroying the hazardous carbon containing compounds in water. Hence, there is still a need for a method and apparatus for altering a carbon containing compound in an aqueous mixture.